1. Field
The following description relates to an apparatus for gain calibration of a microphone array and a method thereof, and more particularly, to an apparatus and method capable of adjusting the gain difference between microphones included in a microphone array.
2. Description of the Related Art
As a mobile convergence terminal including high-tech medical equipment such as high precision hearing aids, a mobile phone, UMPC, camcorders, etc. is becoming prevalent today, the demand for application products using a microphone array has been increased. A microphone array is made of multiple microphones to obtain subsidiary features of sound involving directivity, for example, the direction of sound or the location of sound sources in addition to obtaining the sound itself. The directivity is to increase the sensitivity to a sound source signal emitted from a sound source located in a predetermined direction by use of the difference in time taken until sound source signals arrive at each of the multiple microphones constituting the microphone array. If sound source signals are obtained in the above manner using a microphone array, a sound source signal input in a predetermined direction may be enhanced or suppressed.
A beamforming algorithm based noise cancellation method is applied to most algorithms using a microphone array. For example, current studies are directed toward a method of improving a voice call service and recording quality through directivity-noise cancellation, a teleconference system and intelligent conference recording system capable of automatically estimating and tracking the location of a speaker, and a robot technology for tracking a target sound.
However, if a gain mismatch between sensors occurs in most of the beam forming algorithm, the system performance of the beam forming algorithm is degraded. In particular, according to a generalized sidelobe canceller (GSC) algorithm for an adaptive beamformer, when designing a fixed beam former for enhancing a signal of a particular direction and a blocking matrix for suppressing a signal of a direction a particular direction, a gain mismatch between microphones causes signal leakage and distortion of a target sound source and fails to provide noise suppression, and this causes degradation of the performance of GSC. In addition, the gain difference between microphones distorts the shape of beam during a beamforming process, a desired beam is not formed.
Such a gain mismatch between microphones is caused due to characteristic differences between the microphones within the allowable error range set during manufacturing and also can be due to ageing of the microphones due to use. In order to reduce the characteristic differences between the microphones, the manufacturing process needs to be focused on reducing the difference in quality of the microphones, thereby reducing the possibility of a gain mismatch between microphones. However, this gain mismatch reducing method has limitations with respect to a low cost microphone array due to the high cost involved in utilizing this method.